Rotor and permanent magnet electric motor

ABSTRACT

A rotor, which is cylindrically formed of a magnetic body and in which a plurality of magnet embedding holes are annularly formed at predetermined intervals in a circumferential direction, plate-like permanent magnets being embedded in the magnet embedding holes, includes a flux barrier that is disposed toward an outer circumference of the rotor from an circumferential end of each of the magnet embedding holes, and a slit that is disposed to be adjacent to the flux barrier, in which the slit is a long hole extending in a direction of becoming distant from the flux barrier, from an inner circumferential side of the rotor toward an outer circumferential side thereof, and a notch portion is provided on the outer circumference of the rotor opposing the flux barrier in a diameter direction of the rotor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priorities fromJapanese Patent Application No. 2015-213365 filed on Oct. 29, 2015; theentire contents of which are incorporated herein by reference.

FIELD

The present invention relates to a rotor and a permanent magnet electricmotor.

BACKGROUND

In the related art, there is a magnet embedded rotor including a notchportion that is located on an outer circumference between salient polesadjacent to each other; a bridge that is located between the notchportion and a nonmagnetic portion; and a first protrusion that protrudesoutward from the center of the notch portion, in which a radius of eachof the salient poles gradually decreases from the center of the salientpole toward the notch portion, and a radius of the first protrusion isthe same as a radius of the center of each of the salient pole (refer toJP-A-2012-120326).

In the magnet embedded rotor disclosed in JP-A-2012-120326, asillustrated in FIG. 14A, notch portions 217 a and 216 b, and a firstprotrusion 218 a protruding outward from the center between the notchportion 217 a and the notch portion 216 b are formed on an outercircumference between salient poles 211 and 212 of a rotor 210 adjacentto each other. Consequently, an induced voltage waveform generated frompermanent magnets 213 and 214 becomes similar to a sine wave sinceharmonic components are reduced. Therefore, cogging torque is reduced,and thus vibration or noise of an electric motor is reduced. However, inFIG. 14B illustrating an induced voltage waveform when the rotorillustrated in FIG. 14A rotates, two horns appear around each of a peakand a bottom. Consequently, the induced voltage waveform becomes similarto a sine wave, but harmonic components of an induced voltage or coggingtorque is not sufficiently reduced and thus still remains, and vibrationor noise of the electric motor is required to be further reduced.

SUMMARY

The present invention has been made in consideration of thesecircumstances, and an object thereof is to provide a rotor and apermanent magnet electric motor which can minimize uneven rotationduring rotation of a rotor by reducing harmonic components of an inducedvoltage or cogging torque during the rotation of the rotor. As a result,it is possible to provide a rotor and a permanent magnet electric motorcapable of preventing vibration or noise.

In order to solve the above-described problems and to achieve theobject, according to the present invention, there is provided a rotorwhich is cylindrically formed of a magnetic body and in which aplurality of magnet embedding holes are annularly formed atpredetermined intervals in a circumferential direction, plate-likepermanent magnets being embedded in the magnet embedding holes, therotor including a first nonmagnetic portion that is disposed toward anouter circumference of the rotor from an circumferential end of each ofthe magnet embedding holes; and a second nonmagnetic portion that isdisposed to be adjacent to the first nonmagnetic portion. The secondnonmagnetic portion is a long hole extending in a direction of becomingdistant from the first nonmagnetic portion, from an innercircumferential side of the rotor toward an outer circumferential sidethereof, and a notch portion is provided on the outer circumference ofthe rotor opposing the first nonmagnetic portion in a diameter directionof the rotor.

In the rotor according to the present invention, the second nonmagneticportion may be formed by bending an outer circumferential side end ofthe long hole along the outer circumference of the rotor in a directionof becoming distant from the first nonmagnetic portion.

In the rotor according to the present invention, an angle of the notchportion may match a bent angle of the outer circumferential side end ofthe second nonmagnetic portion.

In the rotor according to the present invention, in a case where a gapbetween the first nonmagnetic portion and the notch portion is indicatedby t, and a gap between the second nonmagnetic portion and the outercircumference of the rotor is indicated by T, the following expressionmay be satisfied:

1.5t≦T≦2.5t

According to the present invention, there is provided a permanent magnetelectric motor including the rotor; and a yoke teeth stator that isdisposed on the outer circumferential side of the rotor and in whichconductive wires are respectively wounded on a plurality of teethextending toward the inner circumferential side from an annular yoke.

According to the present invention, it is possible to minimize unevenrotation by minimizing harmonic components of an induced voltage orcogging torque when a rotor rotates. As a result, it is possible toachieve an effect of being capable of preventing vibration or noise whenthe rotor rotates.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view illustrating a configuration of a permanent magnetelectric motor according to the present example.

FIG. 2A is an enlarged view of an inter-pole portion of a rotorillustrated in FIG. 1.

FIG. 2B is an induced voltage waveform diagram in a case where a slitand a flux barrier of the rotor are formed at a position satisfying arelationship of T=2t.

FIG. 2C is an induced voltage waveform diagram in a case where the slitand the flux barrier of the rotor are formed at a position satisfying arelationship of T=2.2t.

FIG. 3A is a magnetic flux line diagram illustrating changes in magneticflux lines when the rotor illustrated in FIG. 1 rotates inside a stator.

FIG. 3B is a magnetic flux line diagram illustrating changes in magneticflux lines when the rotor illustrated in FIG. 1 rotates inside thestator.

FIG. 3C is a magnetic flux line diagram illustrating changes in magneticflux lines when the rotor illustrated in FIG. 1 rotates inside thestator.

FIG. 3D is a magnetic flux line diagram illustrating changes in magneticflux lines when the rotor illustrated in FIG. 1 rotates inside thestator.

FIG. 4 is a line diagram illustrating changes in harmonic components ofan induced voltage waveform and cogging torque when changing a dimensionof a gap L between a root of a first hole part of the slit and the fluxbarrier illustrated in FIG. 2A.

FIG. 5 is a line diagram illustrating changes in harmonic components ofan induced voltage waveform and cogging torque when changing a length ofa second hole of the slit illustrated in FIG. 2A.

FIG. 6A is a plan view of a rotor as a comparative example in which abent tip part of the slit illustrated in FIG. 2A is lengthened.

FIG. 6B is a U-phase induced voltage waveform diagram in the rotorillustrated in FIG. 6A.

FIG. 7A is a plan view of a rotor as a comparative example in which aninner circumferential side R of a bent portion of the slit illustratedin FIG. 6A is made large.

FIG. 7B is a U-phase induced voltage waveform diagram in the rotorillustrated in FIG. 7A.

FIG. 8A is a plan view of a rotor as a comparative example in which theslits illustrated in FIG. 2A are formed in a V shape without bending thetip parts thereof.

FIG. 8B is a U-phase induced voltage waveform diagram in the rotorillustrated in FIG. 8A.

FIG. 9A is a magnetic flux line diagram illustrating changes in magneticflux lines when the rotor illustrated in FIG. 8A rotates inside thestator.

FIG. 9B is a magnetic flux line diagram illustrating changes in magneticflux lines when the rotor illustrated in FIG. 8A rotates inside thestator.

FIG. 9C is a magnetic flux line diagram illustrating changes in magneticflux lines when the rotor illustrated in FIG. 8A rotates inside thestator.

FIG. 9D is a magnetic flux line diagram illustrating changes in magneticflux lines when the rotor illustrated in FIG. 8A rotates inside thestator.

FIG. 10A is a plan view of a rotor as a comparative example in whichthere are no notch portion and protrusion on an outer circumferencebetween salient poles adjacent to each other, and a slit in which a tippart of a nonmagnetic portion extends and is bent inward in acircumferential direction is formed around both ends of each of salientpoles.

FIG. 10B is a U-phase induced voltage waveform diagram in the rotorillustrated in FIG. 10A.

FIG. 11A is a plan view of a rotor as a comparative example in whichthere are no notch portion and protrusion on an outer circumferencebetween salient poles adjacent to each other, and a slit having the sameshape as in FIG. 2A is formed at the same position.

FIG. 11B is a U-phase induced voltage waveform diagram in the rotorillustrated in FIG. 11A.

FIG. 12A is a plan view of a rotor as Example in which the tip part ofthe slit illustrated in FIG. 2A is bent in an inner circumferentialdirection.

FIG. 12B is a U-phase induced voltage waveform diagram in the rotorillustrated in FIG. 12A.

FIG. 13A is a plan view of a rotor as Example in which a triangular slitis formed to be parallel to the nonmagnetic portion and the outercircumference around both ends of each of the salient poles.

FIG. 13B is a U-phase induced voltage waveform diagram in the rotorillustrated in FIG. 13A.

FIG. 14A is a plan view illustrating one configuration example of arotor of the related art.

FIG. 14B is a U-phase induced voltage waveform diagram during rotationof a permanent magnet electric motor using the rotor illustrated in FIG.14A.

FIG. 15A is a magnetic flux line diagram illustrating changes inmagnetic flux lines when the rotor illustrated in FIG. 14A rotatesinside a stator.

FIG. 15B is a magnetic flux line diagram illustrating changes inmagnetic flux lines when the rotor illustrated in FIG. 14A rotatesinside the stator.

FIG. 15C is a magnetic flux line diagram illustrating changes inmagnetic flux lines when the rotor illustrated in FIG. 14A rotatesinside the stator.

FIG. 15D is a magnetic flux line diagram illustrating changes inmagnetic flux lines when the rotor illustrated in FIG. 14A rotatesinside the stator.

DESCRIPTION OF EMBODIMENTS

Hereinafter, Examples of a rotor and a permanent magnet electric motoraccording to the present invention will be described in detail withreference to the drawings. The present invention is not limited to theExamples.

EXAMPLES

FIG. 1 is a plan view illustrating a configuration of a permanent magnetelectric motor according to the present example. FIG. 2A is an enlargedview of an inter-pole portion of a rotor illustrated in FIG. 1. FIG. 2Bis an induced voltage waveform diagram in a case where a slit and a fluxbarrier of the rotor are formed at a position satisfying a relationshipof T=2t. FIG. 2C is an induced voltage waveform diagram in a case wherethe slit and the flux barrier of the rotor are formed at a positionsatisfying a relationship of T=2.2t. FIGS. 3A to 3D are magnetic fluxline diagrams illustrating changes in magnetic flux lines when the rotorillustrated in FIG. 1 rotates inside a stator.

Rotor of the Present Example

As illustrated in FIG. 1, a permanent magnet electric motor 40 accordingto the present example is provided with a rotor iron core 22 which isformed in a cylindrical shape by laminating a plurality of silicon steelsheets as soft magnetic body steel sheets, and a plurality of magnetembedding holes 12 a, 12 b, 12 c, 12 d, 12 e and 12 f which areannularly formed in a circumferential direction of the rotor iron core22 at predetermined intervals. The permanent magnet electric motor 40includes a rotor 10 provided centering on a rotation shaft 21, and astator 30 surrounding an outer circumference of the rotor 10. In thestator 30, nine teeth 32 which are disposed from the outer circumferenceof the rotor 10 with a predetermined air gap therebetween and extendinward from an annular yoke 31 are formed at intervals of 40 deg(mechanical angle), and tip edges 33 protrude from tips of the teeth 32in the circumferential direction.

In the rotor 10 according to the present example, permanent magnets 13a, 13 b, 13 c, 13 d, 13 e and 13 f are respectively embedded in themagnet embedding holes 12 a to 12 f formed in the rotor iron core 22. Inorder to prevent magnetic-flux short circuiting, voids as firstnonmagnetic portions, that is, flux barriers 14 a to 14 f and 15 a to 15f are formed at both ends of the magnet embedding holes 12 a to 12 f(both ends of the magnet embedding holes extending in thecircumferential direction of the rotor iron core 22). The flux barriers14 a to 14 f and 15 a to 15 f as the first nonmagnetic portions aredisposed toward the outer circumference of the rotor 10. Notch portions16 a to 16 f and 17 a to 17 f are formed on the outer circumference ofthe rotor 10 opposing the first nonmagnetic portions in a diameterdirection of the rotor 10. Consequently, salient poles 11 a to 11 f areformed on outer circumferential sides of the magnet embedding holes 12 ato 12 f.

According to the present example, in the rotor 10, protrusions 18 a to18 f protruding outward may be respectively formed between the notchportions 17 a and 16 b, between the notch portions 17 b and 16 c,between the notch portions 17 c and 16 d, between the notch portions 17d and 16 e, between the notch portions 17 e and 16 f, and between thenotch portions 17 f and 16 a. If the notch portions 16 a to 16 f and 17a to 17 f, and the protrusions 18 a to 18 f are formed on the outercircumference of the rotor 10, harmonic components of an induced voltagegenerated by the permanent magnets 13 a to 13 f are reduced so that aninduced voltage waveform becomes similar to a sine wave, and thuscogging torque is reduced as in JP-A-2012-120326. However, as in aninduced voltage waveform illustrated in FIG. 14B, the waveform has hornsaround the peak and bottom, and thus vibration or noise during rotationof the electric motor cannot be sufficiently reduced.

Therefore, in the present example, the notch portions 16 a to 16 f and17 a to 17 f and the protrusions 18 a to 18 f are formed on the outercircumference of the rotor 10, and slits 19 a to 19 f and 20 a to 20 fas second nonmagnetic portions which are disposed to be adjacent to theflux barriers 14 a to 14 f and 15 a to 15 f are formed at the salientpoles 11 a to 11 f.

Specifically, the slits 19 a to 19 f and 20 a to 20 f are formed at thesalient poles 11 a to 11 f so as to be adjacent to the flux barriers 14a to 14 f and 15 a to 15 f at both ends of the salient poles 11 a to 11f. A shape and arrangement of the slit 20 f will be described by usingthe slit 20 f illustrated in FIG. 2A. The slit 20 f of the rotor 10according to the present example is formed of a first hole part 20 f-1disposed toward the rotor outer circumference from the end vicinity ofthe magnet embedding hole 12 f, an outer circumferential side end partbent along the outer circumference of the rotor at a bent part 20 f-3,and a second hole part 20 f-2 further extending. Since the slits 19 a to19 f and 20 a to 20 f configured in the above-described way are combinedwith the rotor provided with the notch portions 16 a to 16 f and 17 a to17 f and the protrusions 18 a to 18 f, it is possible to remove thehorns occurring around the peak and the bottom of the induced voltagewaveform, which cannot be removed with only the notch portions and theprotrusions, and thus to obtain a waveform similar to a sine wave.

The first hole part 20 f-1 is inclined and disposed to become distantfrom the flux barrier 15 f toward the outer circumference when disposedtoward the rotor outer circumference from the end vicinity of the magnetembedding hole 12 f (that is, when disposed toward the outercircumference from the inner circumference of the rotor).

An inclination of the first hole part 20 f-1 of the slit 20 f of thepresent example is formed to be parallel to an inclination of a notchsurface 17 f-1 of the notch portion 17 f as illustrated in FIG. 2A, andthe second hole part 20 f-2 is formed to be parallel to the outercircumference 10 a. In other words, the slit 20 f of the rotor of thepresent example is inclined so that a bent angle thereof (an angleformed between the first hole part 20 f-1 and the second hole part 20f-2) matches an angle of the notch portion 17 f (an angle formed betweenthe outer circumference 10 a of the rotor 10 and the notch surface 17f-1). A gap between a second hole part 19 a-2 of the slit 19 a and theouter circumference 10 a is indicated by T (a gap between the secondhole part 20 f-2 of the slit 20 f and the outer circumference 10 a isalso indicated by T); a gap between a first hole part 19 a-1 of the slit19 a and an extension line (dashed line) of a notch surface 16 a-1 ofthe notch portion 16 a is indicated by T′ (a gap between the first holepart 20 f-1 of the slit 20 f and an extension line of the notch surface17 f-1 of the notch portion 17 f is also indicated by T′); a gap betweena root of the first hole part 20 f-1 of the slit 20 f and the fluxbarrier 15 f is indicated by L; and an angle from a central line Pbetween (an inter-pole portion) the salient poles 11 f and 11 a adjacentto each other to the bent part 20 f-3 is indicated by θ2. An angle fromthe central line P to a tip part of the second hole part 20 f-2 of theslit 20 f is indicated by θ1. A gap of a bridge between the flux barrier14 a and the notch portion 16 a is indicated by t (a gap of a bridgebetween the flux barrier 15 f and the notch portion 17 f is alsoindicated by t). The Example illustrated in FIG. 2A corresponds to abase model, in which T=1.0 mm, T′=1.1 mm, and L=1.1 mm are set. Arelationship of T=2.2t is assumed to be satisfied, and θ1-θ2=8.55 deg(electrical angle) is set.

FIG. 2B illustrates an induced voltage waveform in a case where the slitand the flux barrier of the rotor are formed at a position satisfying arelationship of T=2t. FIG. 2C illustrates an induced voltage waveform ina case where the slit and the flux barrier of the rotor are formed at aposition satisfying a relationship of T=2.2t. Both of the waveforms aresimilar to a sine wave compared with the waveform illustrated in FIG.14B. Particularly, in a case where the relationship of T=2.2tillustrated in FIG. 2C is satisfied, a smooth waveform similar to a sinewave is obtained. Consequently, harmonic components of an inducedvoltage generated by the permanent magnets are reduced so that coggingtorque is also reduced, and thus vibration or noise of the electricmotor is reduced.

The relationship of T=2.2t is satisfied in the base model illustrated inFIG. 2A, but, as a result of simulation performed by variously changingthe gaps T and t, the harmonic components and the cogging torque changeas follows:

In other words,

in a case of T=t: the harmonic components=3.58%, and the coggingtorque=0.06 Nm

in a case of T=1.5t: the harmonic components=2.79%, and the coggingtorque=0.10 Nm

in a case of T=2t: the harmonic components=2.42%, and the coggingtorque=0.20 Nm

in a case of T=2.2t: the harmonic components=2.31%, and the coggingtorque=0.23 Nm

in a case of T=2.5t: the harmonic components=2.62%, and the coggingtorque=0.28 Nm

in a case of T=3t: the harmonic components=3.39%, and the coggingtorque=0.31 Nm

The harmonic components in FIG. 14A illustrating a case where the slitis not provided are 4.06% as illustrated in FIG. 14B. Here, according tothe results, the slit is provided, and thus the harmonic components arereduced. If the harmonic components are 3% or less, a reduction effectof 1% or more can be achieved compared with a case where the slit is notprovided. If a range of T causing the harmonic components to be equal toor less than 3% is obtained, the following expression is satisfied.

1.5t≦T≦2.5t

Therefore, the slit is preferably formed at a position where T satisfiesthis relationship.

When magnetic flux lines (illustrated in FIGS. 3A to 3D) obtained whenthe rotor according to the present example rotates inside the stator arecompared with magnetic flux lines (illustrated in FIGS. 15A to 15D)obtained when the rotor of the related art provided with the notchportions and the protrusions rotates inside the stator, in a case of thepresent example in which the slit is formed, magnetic fluxes generatedfrom the permanent magnets concentrate on the centers of the salientpoles by the slit as illustrated in FIGS. 3A to 3D, and thus magneticfluxes flowing through the teeth sides (refer to the reference numeral32 in FIG. 1) increase at the centers of the salient poles but decreaseon the inter-pole portion sides. Consequently, an induced voltagewaveform becomes a sine waveform, and thus harmonic components arereduced.

In Case of Changing Length of Second Hole Part

FIG. 4 is a line diagram illustrating changes in harmonic components ofan induced voltage waveform and cogging torque when changing only adimension of the gap L between the root of the first hole part of theslit and the flux barrier illustrated in FIG. 2A. FIG. 5 is a linediagram illustrating changes in harmonic components of an inducedvoltage waveform and cogging torque when changing a length of the secondhole part of the slit illustrated in FIG. 2A.

FIG. 4 illustrates changes in the harmonic components (EMF harmonics[%]) of an induced voltage waveform and the cogging torque [Nm] whenonly a dimension of the gap L between the root of the first hole part 20f-1 of the slit 20 f and the flux barrier 15 f is changed to 0.6 mm toaround 2.4 mm with respect to the base model illustrated in FIG. 2A.Since T′ is fixed, a position of the notch surface 16 a-1 is alsochanged due to the change of L. In FIG. 4, a solid line indicates EMFharmonics, and a dashed line indicates cogging torque. According to theline diagram shown in FIG. 4, the cogging torque is 0.3 Nm or less, andthe EMF harmonics are 3% or less in the entire range, at L of 1 mm ormore. The EMF harmonics are 2.5% or less at L in the range of 0.75 mm to1.7 mm. Thus, L is preferably 1 mm to 1.7 mm, and, particularly, L ismore preferably around 1.1 mm at which the EMF harmonics are low, andintersection with the line of the cogging torque occurs.

FIG. 5 illustrates changes in the harmonic components (EMF harmonics[%]) of an induced voltage waveform and the cogging torque [Nm] whenonly θ1-θ2 (electrical angle) [deg] is changed to 0 deg to around 20 degwith respect to the base model illustrated in FIG. 2A. Also in FIG. 5, asolid line indicates EMF harmonics, and a dashed line indicates coggingtorque. According to the line diagram shown in FIG. 5, the EMF harmonicsare 3% or less at the electrical angle θ1-θ2 in the range of 2.5 deg to15 deg. The cogging torque is 0.3 Nm or less at the electrical angleθ1-θ2 of 2.5 deg or more. Thus, the electrical angle θ1-θ2 preferablyhas the range of 2.5 deg to 15 deg. In other words, as illustrated inFIG. 6A, in a case where the bent tip parts of the slits 20 f and 19 aillustrated in FIG. 2A further extend, the slits are preferably formedin the preferable range of L illustrated in FIG. 4 and the range of theelectrical angle θ1-θ2 illustrated in FIG. 5.

Example in which Inner Circumferential Side R of Bent Part of SlitIllustrated in FIG. 6A is Made Large

A slit shape illustrated in FIG. 7A is substantially the same as theslit shape illustrated in FIG. 6A, but is different therefrom in thatinner circumferential sides of bent parts 79 a-3 and 80 a-3 are formedin an arc shape. An obtained induced voltage waveform is illustrated inFIG. 7B, the harmonic components are 2.88%, and the cogging torque is0.33 Nm. Therefore, it is possible to achieve substantially the sameeffect as in the case of FIG. 6A. In other words, a change of a slitarea of the bent inner circumferential side hardly influences an inducedvoltage waveform or characteristics.

Example in which Slit is Formed in C Shape without Being Bent

FIG. 8A illustrates a rotor as a comparative example in which slits 90 aand 100 a of a rotor 90 are formed in a V shape without bending tipparts thereof unlike the rotor illustrated in FIG. 2A. A waveformillustrated in FIG. 8B corresponds to an induced voltage waveform in acase where the tip parts of the slits are not bent unlike the slits ofthe rotor illustrated in FIG. 2A. In an induced voltage waveform, therotor 90 illustrated in FIG. 8A is provided with notch portions 97 a and96 b and a protrusion 98 a between the notch portions, but a shape ofthe slits 90 a and 100 a combined therewith is a V shape, and thus theharmonic components are 3.22%, and the cogging torque is 0.31 Nm.

The magnetic flux lines (illustrated in FIGS. 3A to 3D) obtained whenthe rotor illustrated in FIG. 2A rotates inside the stator are comparedwith magnetic flux lines (illustrated in FIGS. 9A to 9D) obtained whenthe rotor in which the notch portions and the protrusions are combinedwith the V-shaped slits rotates inside the stator. In FIGS. 3A to 3Dillustrating the bent slits, the bent parts of the slits furthersuppress divergence of magnetic fluxes generated from the permanentmagnets so that magnetic fluxes flowing toward the teeth sides areuniformized, and thus harmonic components of an induced voltage waveformare reduced. In contrast, in a case where the slits are not bent in a Vshape, the slit portions suppress divergence of magnetic fluxesgenerated from the permanent magnets to some extent so that magneticfluxes flowing toward the teeth sides are uniformized, but the bentslits more reduce harmonic components of an induced voltage waveform.

Comparative Example in which there is no Notch Portion and Protrusion,Tip Part of Flux Barrier Extends Inward in Circumferential Direction,and Bent Slits are Formed Around Both Ends of Salient Pole

As illustrated in FIG. 10A, in a case where a rotor 110 has no notchportion and protrusion on an outer circumference thereof, and thus has aperfectly circular shape, the tendency that cogging torquecharacteristics deteriorate is observed. In characteristics of the rotor110 illustrated in FIG. 10A, the harmonic components are 3.23%, and thecogging torque is 0.57 Nm. In the rotor 110 illustrated in FIG. 10A, tipparts of flux barriers 114 a and 115 a extend inward in acircumferential direction, and bent slits 119 a and 120 a are formed. Ascan be seen from an induced voltage waveform illustrated in FIG. 10B,two horns appear around each of a peak and a bottom, and thus thewaveform is not similar to a sine wave.

Comparative Example in which Slits Having the Same Shape as in thePresent Example (FIG. 2A) are Formed without Notch Portion andProtrusion

In a rotor 130 illustrated in FIG. 11A, slits are formed in the sameshape as the shape of the slits of the rotor 10 of the present exampleat the same position, and there are no notch portion and protrusion onan outer circumference thereof. In this case, characteristics of therotor are checked. In a case where there is no notch portion on theouter circumference, as can be seen from an induced voltage waveformillustrated in FIG. 11B, the waveform is considerably different from asine wave. Characteristics of the rotor 130 illustrated in FIG. 11Anotably deteriorate since the harmonic components are 10.62%, and thecogging torque is 0.58 Nm. As mentioned above, in a case where there areno notch portion and protrusion on the outer circumference of the rotor,effects of the slits cannot be achieved even if the same slits as in thepresent example illustrated in FIG. 2A are formed.

Example in which Tip Part of Slit is Bent in Inner CircumferentialDirection

A rotor 170 illustrated in FIG. 12A is the same as the rotor illustratedin FIG. 2A in that notch portions 177 a and 176 b and a protrusion 178 aare formed on an outer circumference thereof, and first hole parts 179a-1 and 180 a-1 of slits 179 a and 180 a are the same as those of theslits illustrated in FIG. 2A, but the slits are different therefrom inthat tip parts of the slits are bent from bent parts 179 a-3 and 180 a-3and extend in an inner circumferential direction and thus second holeparts 179 a-2 and 180 a-2 are formed. In other words, bent angles of thesecond hole parts 179 a-2 and 180 a-2 of the slits 179 a and 180 a arechanged. As illustrated in FIG. 12B, an induced voltage waveform in thiscase has two horns around each of a peak and a bottom, and thus is notsimilar to a sine wave. As characteristics of the rotor, the harmoniccomponents are 3.18%, and the cogging torque is 0.30 Nm. As mentionedabove, the characteristics change just by changing the bent angles ofthe second hole parts 179 a-2 and 180 a-2 of the slits illustrated inFIG. 2A.

Example in which Triangular Slit is Formed

In a rotor 190 illustrated in FIG. 13A, notch portions 197 a and 196 band a protrusion 198 a are formed on an outer circumference thereof, andtriangular slits 199 a and 200 a are formed at both ends of a salientpole 191. The slits 199 a and 200 a are formed in a triangular shape byfirst sides 199 a-1 and 200 a-1 formed to be parallel to flux barriers192 and 193, second sides 199 a-2 and 200 a-2 formed to be parallel toan outer circumference 194, and third sides 199 a-3 and 200 a-3. Aninduced voltage waveform for the rotor 190 illustrated in FIG. 13A isillustrated in FIG. 13B, and it is possible to achieve substantially thesame effect as in the induced voltage waveform illustrated in FIG. 2C.As characteristics of the rotor 190 illustrated in FIG. 13A, theharmonic components are 2.76%, and the cogging torque is 0.26 Nm.

As described above, in the rotor and the permanent magnet electric motorof the related art, at least the notch portion is provided on the outercircumference of the inter-pole portion of the rotor. In a case where aprotrusion is further provided, an induced voltage waveform generatedfrom the permanent magnets of the permanent magnet electric motorbecomes similar to a sine wave since harmonic components are reduced.Consequently, cogging torque is reduced, and thus vibration or noise ofthe electric motor is reduced to some extent. However, in a case wherefurther improvement is intended to be performed, it has not beenperformed up to now to improve characteristics by using a notch portionor a protrusion and a slit shape, or a combination with arrangementthereof. Particularly, as examined through comparison between therespective Examples and the comparative examples, the effect achieved byproviding the notch portion or the protrusion and the effect achieved byproviding the slit are not led to a result of simply adding the effectstogether. Since characteristics may deteriorate depending on a shape orarrangement of the slit, even a person skilled in the art cannot easilyconceive of patterning of a specific slit shape or an arrangementposition as in the present example.

In the rotor according to the present invention, at least a notchportion may be provided on a rotor outer circumference of an inter-poleportion at which a flux barrier as a first nonmagnetic portion isdisposed in an outer circumferential direction of the transport, and aprotrusion may be further provided at the inter-pole portion. Ifharmonic components of an induced voltage generated in conductive wireswound on the teeth by the permanent magnets of the rotor are reduced, aninduced voltage waveform becomes similar to a sine wave. The inducedvoltage waveform becomes similar to a sine wave so that the coggingtorque is reduced, and thus uneven rotation is minimized when the rotorrotates. If the uneven rotation is minimized, vibration or noise of theelectric motor is reduced. In order to use this phenomenon, in the rotoraccording to the present invention, the slit as a second nonmagneticportion is disposed to extent from a position adjacent to the fluxbarrier in the outer circumferential direction of the rotor. The slit isformed of a first hole part as a long hole extending in the outercircumferential direction, a bent part in which an outer circumferentialside tip part of the first hole part is bent along the outercircumference of the rotor from an end of the magnet embedding holetoward the center, and a second hole part further extending along theouter circumference.

The slit of the rotor is inclined so that an angle of the notch portionformed on the rotor outer circumference matches a bent angle of thefirst hole part of the slit. The second hole part of the slit is bent atthe bent part so as to extend in parallel to the rotor outercircumference.

In relation to the slit of the rotor, in a case where a distance betweenthe flux barrier and the notch portion formed on the rotor outercircumference is indicated by t, and a distance between the second holepart of the slit and the rotor outer circumference is indicated by T,the flux barrier and the slit are disposed at positions satisfying thefollowing expression.

1.5t≦T≦2.5t

A rotor and a permanent magnet electric motor using the rotor areconfigured as described above. Therefore, in a case where at least anotch portion is provided on a rotor outer circumference, and also in acase where a protrusion is further provided at an inter-pole portion, aninduced voltage waveform generated from permanent magnets of thepermanent magnet electric motor can be made to become similar to a sinewave by reliably reducing the harmonic components. Consequently, thecogging torque is reduced. Thus, vibration or noise of the electricmotor is reduced.

As Example of the present invention, for example, a description has beenmade of a case where the permanent magnet electric motor is used for aninterior permanent magnet synchronous motor (IPMSM) 40 with six polesincluding the rotor 10 and the stator 30 as a compressor motor which hasa small size and requires strong torque, but the present invention isnot necessarily limited thereto. The permanent magnet electric motor ofthe present invention is applicable to the interior permanent magnetsynchronous motor 40 having four or more poles.

As described above, in the rotor and the permanent magnet electric motoraccording to the present invention, an induced voltage waveform becomessimilar to a sine wave so that the cogging torque is reduced, and thusthe permanent magnet electric motor is useful as a permanent magnetelectric motor which is driven at a high rotation speed, particularly,such as an electric motor built into a compressor.

What is claimed is:
 1. A rotor which is cylindrically formed of amagnetic body and in which a plurality of magnet embedding holes areannularly formed at predetermined intervals in a circumferentialdirection, plate-like permanent magnets being embedded in the magnetembedding holes, the rotor comprising: a first nonmagnetic portion thatis disposed toward an outer circumference of the rotor from ancircumferential end of each of the magnet embedding holes; and a secondnonmagnetic portion that is disposed to be adjacent to the firstnonmagnetic portion, wherein the second nonmagnetic portion is a longhole extending in a direction of becoming distant from the firstnonmagnetic portion, from an inner circumferential side of the rotortoward an outer circumferential side thereof, and wherein a notchportion is provided on the outer circumference of the rotor opposing thefirst nonmagnetic portion in a diameter direction of the rotor.
 2. Therotor according to claim 1, wherein the second nonmagnetic portion isformed by bending an outer circumferential side end of the long holealong the outer circumference of the rotor in a direction of becomingdistant from the first nonmagnetic portion.
 3. The rotor according toclaim 1, wherein an angle of the notch portion matches a bent angle ofthe outer circumferential side end of the second nonmagnetic portion. 4.The rotor according to claim 2, wherein an angle of the notch portionmatches a bent angle of the outer circumferential side end of the secondnonmagnetic portion.
 5. The rotor according to claim 1, wherein, in acase where a gap between the first nonmagnetic portion and the notchportion is indicated by t, and a gap between the second nonmagneticportion and the outer circumference of the rotor is indicated by T, thefollowing expression is satisfied:1.5t≦T≦2.5t
 6. The rotor according to claim 2, wherein, in a case wherea gap between the first nonmagnetic portion and the notch portion isindicated by t, and a gap between the second nonmagnetic portion and theouter circumference of the rotor is indicated by T, the followingexpression is satisfied:1.5t≦T≦2.5t
 7. The rotor according to claim 3, wherein, in a case wherea gap between the first nonmagnetic portion and the notch portion isindicated by t, and a gap between the second nonmagnetic portion and theouter circumference of the rotor is indicated by T, the followingexpression is satisfied:1.5t≦T≦2.5t
 8. A permanent magnet electric motor comprising: the rotoraccording to claim 1; and a yoke teeth stator that is disposed on theouter circumferential side of the rotor and in which conductive wiresare respectively wounded on a plurality of teeth extending toward theinner circumferential side from an annular yoke.
 9. A permanent magnetelectric motor comprising: the rotor according to claim 2; and a yoketeeth stator that is disposed on the outer circumferential side of therotor and in which conductive wires are respectively wounded on aplurality of teeth extending toward the inner circumferential side froman annular yoke.
 10. A permanent magnet electric motor comprising: therotor according to claim 3; and a yoke teeth stator that is disposed onthe outer circumferential side of the rotor and in which conductivewires are respectively wounded on a plurality of teeth extending towardthe inner circumferential side from an annular yoke.
 11. A permanentmagnet electric motor comprising: the rotor according to claim 4; and ayoke teeth stator that is disposed on the outer circumferential side ofthe rotor and in which conductive wires are respectively wounded on aplurality of teeth extending toward the inner circumferential side froman annular yoke.